All of the following crops are grown in the North Central Plains except: a. fruits
b. coffee
C. peanuts
d. vegetables

B

Coffee is grown in central areas near the equator.

Three things why a study can be considered invalid might be:

Lack of Research: if a study does not achieve the requirements of the research method then it is not valid.  

Biased opinions: if a study is based on one specific way of the researcher then in characterized as invalid.  

No evidence: if the study does not have enough or not at all evidence of what it was investigated then it cannot be reliable and so, invalid.